Added DisksRecovering

[Finomosec]

Hi,

after running mdadm --replace /dev/sdb1 --with /dev/sdk1 the output of cat /proc/mdstat looks like this:

Personalities : [raid6] [raid5] [raid4] [raid0] [raid1] [raid10]
md0 : active raid5 sdk1[6](R) sdf1[5](S) sdg1[4] sdc1[2] sde1[1] sdb1[0]
      14650718208 blocks super 1.2 level 5, 512k chunk, algorithm 2 [4/4] [UUUU]
      [>....................]  recovery =  1.4% (72694748/4883572736) finish=1601.3min speed=50071K/sec
      bitmap: 0/37 pages [0KB], 65536KB chunk

unused devices: <none>

Sidenote:

• DisksTotal reports 4 (taken from the [4/4])
• DisksSpare reports 1 taken from the (S)
• But The (R) disk does not show up anywhere
• So my Prometheus/Grafana report shows only 5 disks, even though there are actually 6.

I added support for recovering (R) disks as DisksRecovering.

Can you please merge it (and adjust the test-cases - i don't have the environment to run them)?

[Finomosec]

Manual test passed.

I integrated it with node_exporter (locally patched version) and it works!

[Finomosec]

I just found this other PR, which kind of includes my change.
Also, i got one thing wrong: (R) seems to stand for Replacement, not Recovering.

See here: https://github.com/prometheus/procfs/pull/674/files#r1803915063

[Finomosec]

Due to my misunderstanding (see previous comment) and the other open PR #674, which also solves my problem, i withdraw my PR.